Quantitative estimates of the human health hazards posed by toxic metals in the environment play the key role in setting realistic exposure standards and in devising efficient preventive measures. Three recognized heavy metals provide the focus for this program project: mercury (both as methylmercury and as metallic mercury vapor), cadmium and lead. Since toxicity is typically both defined and determined by multiple factors, the research plan is also multidimensional. It encompasses investigations of the physical and chemical properties of metals and metal compounds that determine how they enter the body; of how they are handled (distributed, metabolized) by the body and its organ systems; of their capacity to impair the processes of reproduction and development; of their action on behavior and the nervous system; of their potential for tissue pathology; of their impact on the health of selected human populations.